When the iPhone 4S was launched in 2011 all of the attention was on Siri, Apple's voice assistant.

There didn't seem to be much else to talk about; the new phone was simply a faster clone of the previous year's model.

Siri turned out to be a disappointment, failing to understand Scottish accents properly until the update in September this year. But buried inside the iPhone 4S was a much more important technological advance - Bluetooth 4.0.

Largely ignored at the time, Bluetooth 4.0 is backward compatible with traditional Bluetooth devices such as in-car hands-free kits and speaker docks, but it also has a low-energy model called Bluetooth LE (or BLE). While the battery life of regular Bluetooth devices can be measured in hours, BLE devices can last for months or years on a single coin-sized battery. Innovative products are now appearing that wouldn't have been possible before BLE - everything from watches to houseplants are being given a technological makeover.

Wahoo Fitness has been one of the first adopters of BLE technology, launching a range of wireless fitness gadgets from its base in Atlanta, Georgia. I tested the Blue SC, a cycling speed sensor, and the Blue HR, a chest-mounted heart rate monitor. With the nights drawing in and the wind blowing a hoolie, I fitted the kit to my turbo trainer (a regular bicycle mounted on rollers indoors).

The monitor is a cinch to set up. Download Wahoo's fitness app, attach the Blue HR strap to your chest and the two devices start communicating wirelessly, showing your current and average heart rate on the screen.

Setting up the Blue SC isn't quite as easy, not least because the online-only instructions are hidden from UK visitors. A matchbox-sized gadget measures both wheel speed and cadence (pedaling speed), making placement of the device critical. Two sensor magnets must be fitted to the spokes and pedal cranks, the latter requiring removal of the pedal. On my hybrid the process was made difficult by the gap between the crank and rear wheel, which forced me to mount the Blue SC at a radical angle. That said, it mounted securely and hasn't moved since.

Once set up, the Wahoo system is a joy to use, tap and swipe gestures letting you switch between views including lap times, calories burned and, if you're outdoors, your compass heading. The only remaining question is, if you're outdoors, where do you mount your phone? Wahoo has a couple of options from a rugged handlebar mount (£54.99) to a clever RFLKT wireless display (£119.99) that allows you to keep your phone safely in your pocket.

Wahoo Fitness sensors, £49.99

Rating: 4/5

Positives: Clear, easy-to-read and reliable system.

Negatives: Blue SC can be tricky to set up.